Not sure if I should be worried about this. I wanted a slightly better seat on BA16 (2x Club Suite with Avios and companion voucher)

On the way out I was able to choose. On the way back, although there are other seats free and I can select them, it always fails when I confirm.

I was on live chat for ages with BA and they said they had the same problem, and to try at the airport.

It seems bizarre to me they don’t know why they can’t change the seats, and agree other seats are still available!

Could there be anything wrong with the booking I need to be concerned about?